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[reaction: see text] A concise synthesis of the spinosyn A tricyclic nucleus 27 has been developed by a route featuring a one-pot tandem intramolecular Diels-Alder reaction and intramolecular vinylogous Morita-Baylis-Hillman cyclization in which five stereocenters in tricycle 10 are set with excellent selectivity.
Peptide vinyl sulfones were prepared from 2-chlorotrityl resin-bound phenolic amino vinyl sulfones in high yield and purity. This method enables the convenient synthesis of peptide vinyl sulfones having different amino acids at the P(1) position. It also allows efficient synthesis of vinyl sulfone-containing, activity-based probes of cysteine proteases used in a proteomic experiment.
[reaction: see text] alpha-Lithio cumulenyl ethers can be prepared in situ and converted to alpha-allenyl cyclopentenones. Isomerization of the product of one such reaction has led to a furanyl cyclopentenone, the core structure of nakadomarin A.
A versatile, efficient method for the preparation of alpha-monofluoromethylene (-CHF-) phosphonates from alpha-fluorovinylphosphonate provides access to a class of lysophosphatidic acid (LPA) receptor-subtype agonists. In addition, sn-2 O-methylation of alpha-monofluoromethylene phosphonates using trimethylsilyldiazomethane generated sn-1-acyl, 2-O-methyl alpha-monofluoromethylene derivatives. Finally, a novel method for the selective etherification of 1,2-diols was developed and a new class of sn-1 O-methyl, 2-acyl alpha-monofluoromethylene LPA analogues was prepared. [reaction: see text]
A general method for the coupling of aryl and vinyl halides with diaryl and dialkyl phosphines, as well as with dibutyl phosphite, is reported. This highly efficient transformation is realized through the use of copper(I) iodide as a catalyst, N,N'-dimethylethylenediamine as a ligand, and Cs(2)CO(3) as a base. A variety of sterically hindered and/or functionalized substrates were found to react under these reaction conditions to provide products in good to excellent yields. [reaction: see text]
[reaction: see text] An efficient intermolecular 1,3-dipolar cycloaddition of a variety of nitrones to pentafluorophenyl (PFP) vinylsulfonate is described. The transformation produces stable "reversed" cycloadducts of unprecedented stereo- and regioselectivity. Subsequent amine displacement of the PFP moiety furnished functionalized sulfonamide products in good yields.
[reaction: see text] A general and efficient copper-catalyzed method for the amidation of vinyl bromides and iodides has been developed. This protocol uses a combination of 5 mol % copper iodide and 20 mol % N,N'-dimethyl ethylenediamine. Substrates bearing ester, silyl ether, and amino groups were successfully coupled under the reaction conditions. The double bond geometry of the vinyl halides was retained under the reaction conditions.
[reaction: see text] Additions of vinylic zinc bromide reagents to alpha-chiral aldehydes (R(1) = CH(2)OTBS, R(2) = Me; R(1) = Me, R(2) = OTBS) in the presence of lithiated (+)- or (-)-N-methylephedrine proceed with predominant reagent control to afford anti or syn adducts stereoselectively, except when the aldehydes possess an alkoxy substituent at the alpha- or beta-positions (R(1) = Me, R(2) = OBn; R(1) = CH(2)OBn, R(2) = Me), in which case chelation-controlled adducts predominate.
Tricyclic erythromycin A derivatives are known potent antibacterial agents, but the potential of substituted tricyclic erythromycin A derivatives remains largely unexplored. To study this lead, the tricyclic ring system was synthesized by an efficient three-step synthesis starting from the allylic alcohol utilizing a novel azidoisocyanate. These tricyclic analogues can be used as scaffolds to probe secondary ribosomal binding sites. [structure: see text]
Substituted carbazoles are readily prepared in good yields by the palladium-catalyzed cross-coupling of alkynes and N-(3-iodophenyl)anilines. This process proceeds by carbopalladation of the alkyne, heteroatom-directed vinylic to aryl palladium migration, and ring closure involving two consecutive C-H activation processes. The process has also been expanded to the synthesis of an indole. [Structure: see text]
A concise total synthesis of (+)-pseudodistomin D was developed. The absolute stereochemistry was established through a dynamic kinetic asymmetric cycloaddition of an isocyanate to a vinyl aziridine. The piperidine core was constructed through a silver(I)-catalyzed hydroamination of an alkyne and subsequent diastereo- and regioselective reduction. [reaction: see text]
[reaction: see text] Olefin cross-metathesis has been used to prepare alpha-C-galactosylceramide derivatives. The metathesis process merged vinyl and propenyl glycosides with vinyl derivatives of phytosphingosine. The use of ethylene enhanced the yield of the methathesis step.
[reaction: see text] 1,4-Disubstituted 1,2,3-triazoles are obtained in excellent yields by a convenient one-pot procedure from a variety of readily available aromatic and aliphatic halides without isolation of potentially unstable organic azide intermediates.
[reaction: see text] The hydroamination of styrene with aniline catalyzed by phosphine-ligated palladium triflates exhibits a substantial (13)C isotope effect at the benzylic carbon. This supports rate-determining nucleophilic attack of amine on a eta(3)-phenethyl palladium complex. Deuterium exchange observations and predicted isotope effects based on DFT calculations support this mechanism. Selectivity in these reactions is determined by the facility of palladium displacement after reversible hydropalladation of the alkene.
[reaction: see text] Inter- and intramolecular titanium-mediated cyclopropanation reactions of vinylogous esters are reported. Comparison between the Kulinkovich cyclopropanation of esters and vinylogous esters provides mechanistic insight regarding reaction variables such as reaction temperature, solvents, and a Lewis acid additive.
Palladium(II) complexes catalyze the formation of enamides via the formal cross-coupling reaction between nitrogen nucleophiles and vinyl ethers. These vinyl transfer reactions proceed in good yields with amide, carbamate, and sulfonamide nucleophiles, and the optimal catalyst is (DPP)Pd(OCOCF(3))(2) (DPP = 4,7-diphenyl-1,10-phenanthroline). [reaction: see text]
[reaction: see text]. Aluminum and copper Lewis acids were implemented to effect a regioselective [1,3] rearrangement of allylvinyl ethers in moderate to good yields. The use of trisubstituted alkenes leads to depressed levels of Claisen products.
[reaction: see text] Regio- and stereoselective enyne cross metathesis reactions between borylated alkynes and terminal alkenes were realized to provide a variety of functionalized vinyl boronates. High chemical yield and regioselectivity was achieved irrespective of substituents on the alkyne and alkene counterparts, whereas Z/E-selectivity was found to be dependent upon the substituents both on the alkyne and alkene.